Deep drawing is a technique that allows obtaining from planar and essentially thin sheet metal with a specific thickness an object the shape of which is predetermined and is essentially cylindrical and hollow. In this process, the sheet is deep drawn in a deep drawing die by the mechanical action of a punch.
Multistage deep drawing is characterized by being a process comprising several consecutive deep drawing and redrawing operations. Deep drawing is the action of mechanically deforming planar sheet metal against the deep drawing die with the aid of the punch. Redrawing comprises repeated deep drawing stages in which the part is gradually deformed iteratively until reaching the desired final shape.
Sometimes an ironing process is applied after deep drawing stages. Ironing is characterized by being a process which allows reducing the thickness of the wall of the previously deep drawn part and consists of passing the previously deep drawn part through an ironing die.
In the metal working sector, the manufacture of ammunition cartridge cases is done by first performing the deep drawing operations to obtain the inner shape of the part and to subsequently reduce the thickness of the walls and increase the length of the part by means of successive ironing operations. The deep drawing, redrawing and ironing stages are fundamentally defined by means of design rules based on the empirical tests without taking into account the plastic evolution of the material and without considerations concerning the combination of stages or optimization of the process.
The present invention provides a different process that allows manufacturing final parts with different design parameters and an optimized process that substantially improves the results obtained up until now.
This invention is based on the contributions made in the articles entitled “The development of competencies in manufacturing engineering by means of a deep-drawing tool”, “Prediction of the limiting drawing ratio and the maximum drawing load in cup-drawing”, “On multistage deep drawing of axisymmetric components” and “Energia de estirado en deformación homogénea”. The definition of new methods based on aided design capable of improving some results has been the object of patents, such as U.S. Pat. No. 7,623,939 B2 “Method of design a tool for deep drawing and tool for deep drawing of sheet metal”, based on parameterized geometry and on meeting quality criteria.